The invention relates to printing machines in general, and more particularly to improvements in auxiliary or additional printing machines of the type known as imprinters.
It is often necessary to provide or combine a cylinder printing machine with an auxiliary apparatus (imprinter) which is disposed at the discharge end of the main machine and can constitute an additional flexographic printer. As a rule, the imprinter comprises two printing cylinders which flank a single counterpressure cylinder and carry printing plates serving to apply additional printed matter to a running web of paper or other material which issues from the main printing machine. The counterpressure cylinder guides the running web along a preselected path wherein the web can receive printed matter from the one or the other printing cylinder. Each printing cylinder receives printing ink from an ink supplying unit which, in a flexographic imprinter, can comprise a so-called anilox cylinder and a rubber roller. That printing cylinder which carries one or more printing plates is caused to contact the running web while the other printing cylinder is idle (e.g., while the operators exchange the printing plate or plates on the other printing cylinder). The counterpressure cylinder rotates about a fixed axis. The active printing cylinder can be used to apply additional printed matter to certain pages or groups of pages of special editions of newspapers or other types of printed publications, e.g., to local editions of nationally or internationally distributed publications.
An advantage of imprinters is that they constitute a simple, inexpensive and effective means for applying printed matter to a limited number of discrete or coherent sheets which issue from the main printing machine. For example, the two printing cylinders of a conventional imprinter can be used to apply additional printed matter in two different colors or to apply two different types of printed matter in the same color or in different colors.
A drawback of conventional imprinters is that the peripheral speed of each printing cylinder cannot be readily and accurately synchronized with the peripheral speed of the counterpressure cylinder. Thus, if a printing cylinder having a first diameter is to be replaced with a printing cylinder having a different second diameter, it is necessary to exchange a substantial number of gears, antifriction bearings and other parts which are normally mounted in the interior of the frame so that they are not readily accessible. This involves a substantial amount of work by several skilled or highly skilled workmen and entails a longer-lasting stoppage of the entire printing machine. As a rule, a change of the setup takes up several hours.
Another drawback of conventional imprinters is that the starting and stoppage of the cylinders in the imprinter take up an inordinately large amount of time and can be carried out only by relying on complex and expensive instruments. This is also due to the fact that the peripheral speed of a freshly inserted printing cylinder must match exactly the peripheral speed of the counterpressure cylinder.
A further drawback of conventional imprinters is their lack of versatility.